Rotating blowout preventors are known to those skilled in the drilling art, and are usually referred to as RBOP's; or, rotary stripper devices. There is hardly ever a borehole of any significance sunk into the ground without the employment of at least one high pressure rotary stripper device. The RBOP enables a rotating driving member, such as a drill string, or the kelly of a drill string, to be slidably forced axially therethrough. The RBOP includes a stripper rubber assembly rotatably mounted respective to a main body so that the driving member and stripper rubber assembly rotate in low friction relationship respective to the remainder of the RBOP, and at the same time the drill string can be slidably positioned axially respective to the RBOP.
The stripper rubber assembly of the RBOP enables various different sizes of tubular goods to be forced into the borehole and thereafter retrieved from the high pressure interior of the borehole. However, from time to time, a larger or smaller elongated member must be connected within the drill string and placed within the borehole; and, for this and other reasons, the stripper rubber assembly of most all RBOP assemblies is subjected to considerable wear.
RBOP's are usually quite complex, and may include more than a hundred parts. Therefore, the cost of the RBOP usually is directly proportional to its complexity. The RBOP is complex in design because it must be fabricated in such a manner to adequately resist the heavy forces resulting from upthrust and downthrust of the stripper rubber assembly, as well as the lateral forces imposed on the stripper rubber assembly.
Accommodation of the above mentioned forces has been achieved by employing various different large and expensive ball bearings and tapered roller bearing which must be provided with an inside diameter of a size to accommodate the required stripper rubber assembly. The massive bearings require extensive design techniques in order to maintain them in proper operative condition, and in order to achieve a reasonable operational life expectancy. Needless to say, bearings of the required size and design are quite expensive. Accordingly, any improvement which extends the operating life of the RBOP is considered very desirable because of the reduction in cost and because the entire drilling operation relies upon the proper operation of the RBOP.
My previous Patents, U.S. Pat. Nos. 4,154,448; 3,868,832, and 3,724,862 disclose an RBOP which can be advantageously employed as a high pressure rotary stripper. The Murray Patent, U.S. Pat. No. 4,157,186 and the Bunting, et al Patent, U.S. Pat. No. 4,143,880, disclose an RBOP which can also be used in drilling some boreholes. U.S. Pat. Nos. 4,208,056 and 4,367,795 also disclose various different RBOP devices which are advantageously employed during drilling operations. These and other prior art RBOP devices can be used in conjunction with the teachings of the present invention.
The present invention, when used in conjunction with the above mentioned RBOP's, perform more satisfactorily during drilling operations, and the operating cost thereof is appreciably reduced. For this reason, the drilling operation is more dependable because the life of the RBOP is greatly extended by the present invention, and therefore the drilling operation costs are even more reduced because of reduction in downtime.